Production wells on onshore cil fields are not systematically cathodically protected. On the contrary, offshore weils attained from fixed drilling plotforms are necessorily subjected to cathodic protection systems designed for such structures. The design of such systems must Cake into consideration the amount of current demanded by the well, generally considered as parositic current. Different colculoting methods exist, more or less based on scientific considerations. None con truly foresee what the reality will be, and measuring methods have ta be used if we want to check to see exactly what is happening. The different calculating and measuring methods are reviewed and criticized, thus bringing out points that we feel should be further investigated in the future.